Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $86.48   8.762%   $94.0574   $94.06   $94.05   $94.10  
  Purchase #2 $190.78   11.843%   $213.3741   $213.37   $213.35   $213.40  
  Purchase #3 $97.55   5.479%   $102.8948   $102.89   $102.90   $102.90  
  Purchase #4 $6.62   9.607%   $7.256   $7.26   $7.25   $7.30  
  Purchase #5 $170.66   8.775%   $185.6354   $185.64   $185.65   $185.60  
  Purchase #6 $103.25   6.862%   $110.335   $110.34   $110.35   $110.30  
  Purchase #7 $241.75   12.371%   $271.6569   $271.66   $271.65   $271.70  
  7 purchase totals = $897.09       $985.2096   $985.22   $985.20   $985.30